The present invention relates to a main helicopter rotor.
In particular, the present invention relates to a rotor of the type comprising a drive shaft designed to turn about its axis; a hub integral with the drive shaft; a number of blades extending substantially radially outwards from the hub and each having a connection device for connection to the hub; a pitch change device connected to each said connecting device; and means for connecting each said connecting device to the hub, said connecting means comprising a first spherical elastomeric bearing located between a respective connecting device and the hub and defining the focal point of a respective blade.
Known rotors of the aforementioned type are generally referred to as "semirigid", wherein each said connecting device comprises a respective elastic element located between the hub and a respective blade, and designed to absorb both the loads due to centrifugal force and part of the shearing stress.
The main drawback of known rotors of the aforementioned type is the failure of said elastic elements, normally consisting of metal blades integral at one end with the hub and extending radially outwards of the same, to meet the conflicting requirements of relatively low rigidity when the rotor is operative, and relatively high rigidity when the rotor is idle and possibly subjected to wind. In addition to being deformable in flight, in response to the shear exerted on the respective blades, so as to generate the required control moments, said elastic elements are also called upon to support the blades in the correct position in relation to the ground when the rotor is idle.
As such conflicting requirements are rarely, if ever, achievable in actual practice, for supporting the blades when the rotor is idle, known rotors of the aforementioned type usually feature mobile supporting elements of the type normally employed on so-called "articulated" rotors.
A further point to note in connection with known "semirigid" rotors of the aforementioned type is that cyclic and collective pitch control of the blades depends on the torsional deformability of said elastic elements, which must be relatively long for maintaining within acceptable limits the stress exerted by the pitch change controls.
As a consequence of the above, the diameter and, therefore, drag of the hub on known rotors of the aforementioned type are usually considerable.